1. Technical Field of the Invention
The present invention generally relates to plant-derived natural red pigment, and more particularly to anthocyanins from the fruit of Garcinia indica. Still more particularly, the present invention relates to methods of extracting and stabilizing this pigment, and its use as a colorant.
2. Description of Related Art
Natural red color or hues of red color are frequently employed for adjusting the color of various foodstuffs, beverages, pharmaceuticals and the like. Some of the conventional red colorants in use today are derived from insects, for example, cochineal. Other red colorants are synthetic in origin. As a result, many of the existing red colorants have distinct disadvantages with respect to suitability for use in foodstuffs and beverages meant for human consumption.
In recent times, a variety of natural sources of red colorants have been identified and methods for extraction of natural red pigments have been described. For example, a natural red color has been extracted from grape skin and is has been standardized with respect to specific color value and percentage of anthocyanin content. This grape-derived pigment has been stabilized for use in dairy, beverages, and confectionary. While this natural pigment is satisfactory for some purposes, the problem remains that it does not give the precise hues that are desired in some food and beverage products.
U.S. Pat. No. 4,172,902 (Asen et al.) describes a method for extracting an anthocyanin red color from the ‘Heavenly Blue’ morning glory flower. Although morning glories provide an excellent red pigment, the availability of this natural source is too limited for widespread or commercial use. Therefore, there are problems associated with making use of this anthocyanin pigment for coloring foodstuffs and beverages.
U.S. Pat. No. 5,908,650 (Lenoble et al.) describes certain anthocyanin-based colors that are stabilized with respect to loss of color due to pH, heat or light by water-soluble pigment-improving extracts of plant material such as rosemary, sage and peppermint. The active pigment-improving agent is said to be a flavonoid glycuronide or a flavonoid glucuronide.
U.S. Pat. No. 6,132,791 (Fox) describes the extraction of a natural red sunflower anthocyanin colorant that is said to have naturally stabilized color qualities. According to the procedure described in that patent, sunflower hulls are heated in an aqueous solution at pH 2-6. to produce a red juice that is heat and light stable over a pH range of about 1-6.
U.S. Pat. No. 6,180,154 (Wrolstad et al.) describes a natural colorant preparation from potato extract. However, the presence of steroidal glyco-alkaloids in potato introduces the potential for toxicity in red color extracts obtained from red potato. One way to address this problem is to develop a variety of red potato that is lower in the toxic glyco-alkaloid, and to use it for extraction of the red potato pigment.
Japanese Patent Nos. 223756 and 25460 describe studies in which red pigments were extracted from red cabbage and the extracts were evaluated for anthocyanin color values. Although accepted and proven methods for extraction of red color from red cabbage exist, even those methods have practical shortcomings, which preclude the cost effective application of such methods, especially for commercial applications. One such drawback is that methods, which employ alcohol extraction of the red pigment, can leave traces of the alcohol in the product. If alcohol remains in the extract, even in small amounts, it can adversely affect the filtration membrane used for concentration of the pigment extract. Another drawback is that when alkali is used for extraction of color pigments, stability of the pigment solution is badly affected, leading to degradation of the pigment by the alkali. Methods that use sulfuric acid or sulfate liquor for extraction of red coloring from red cabbage have as a shortcoming the generation of sulfur dioxide during heating. Sulfur dioxide production is highly undesirable for environmental safety reasons as well as because of its tendency to form foul smelling sulfur-containing compounds in the final product.
WO 02/14477 describes certain anthocyanin pigments isolated from the fruits of Garcinia indica. 
While the demand for natural red pigment remains high, the existing colorants and their methods of preparation are not able to meet the existing demand. Even though some of the known sources are renewable, or can be grown in great quantity, the supply of satisfactory red colorants is not adequate for current demand. There is still an unmet need for practical red colorant compositions that are safe for human consumption, avoid discoloring or fading, and impart to foods and other products the desired hues.